1. Field of the Invention
The present invention relates to radiation detectors generally and, more particularly, but not by way of limitation, to a novel high efficiency and high homogeneity large-area gas-filled radiation detector.
2. Background Art
All known gas-filled large-area radiation detectors are not free from the problems related to the existence of zones with decreased efficiency. One of the contributing factors is the method of anode wire suspension. The wire suspension system usually uses of some type of holding elements like stand-offs, feedthroughs, etc. All these elements are made from dielectric and/or metal parts that are located in the active volume of a detector. Some of these elements have either direct contact with anode wires or are located close to them.
The principle of operation of all gas filled detectors is based on the phenomenon of so-called gas amplification. The uniformity of the detector response depends on the uniformity of the electric field along the anode wires in the active volume of the detector. Presence of wire suspension elements causes distortions of the electric field that leads to the disturbance of gas amplification and consequently to reduction of radiation detection efficiency. This presence creates usually radially symmetric zones around a suspending element that can be 20 mm or more in diameter and that features significantly reduced detection efficiency. Depending on the detector design, the wire supporting elements are mounted either to the bottom of the detector or to its side walls. In the latter case, the efficiency reduction additionally contributes to the detector end effect problem. For a four-wire system (eight wire supporting elements), the total area of decreased efficiency may be 25 cm2 or more. This may potentially cause significant losses of the overall detection efficiency.
In the health physics radiation detection systems that utilize multiple adjacent detectors (for example, in whole body monitors), detector end effects are as critical as problems within the detector volume since they affect the response uniformity of the whole detector array.
An attempt to solve “dead zones” problems is described in U.S. Pat. No. 3,934,165, issued Jan. 20, 1976, to Meekins, and titled PROPORTIONAL COUNTER END EFFECTS ELIMINATOR.
Technical solutions for large area radiation detectors have not been addressed.
Accordingly, it is a principle object of the present invention to provide a radiation detector that has improved detection homogeneity and minimizes dead zones by eliminating anode wire suspending elements and wire connections from the active volume of the detector and by minimizing side wall thickness.
It is a further object of the present invention to provide such a detector that has thin, flat elements made from a dielectric material that are embedded within the detector side walls, and that do not contribute to the wall thickness which elements are used for anode wire support.
It is another object of the present invention to provide such a detector in which these elements feature small center metal pads on both sides and metal plated hole connecting these pads; allowing mounting anode wires to be placed through the holes using soldering techniques or conductive adhesive, sealing at the same time detector volume from the gas leaks.
It is an additional object of the present invention to provide such a detector having these elements supporting anode wires, playing the role of feedthroughs and electrically connecting anode wires in multiwire applications.
It is yet a further object of the present invention to provide such a detector having connections to readout electronics using cables installed in grooves in the side walls of the detector and which do not contribute to the side wall thickness.
It is yet another object of the present invention to provide such a detector having no feedthroughs in the bottom of the detector.
It is yet an another object of the present invention to provide such a detector that has no feedthroughs or other wire supporting parts in the side walls that would extend into the active volume of the detector or beyond the outer surface of the side walls.
It is yet an additional object of the present invention to provide such a detector that has no dielectric materials along the side walls that in some designs are used to suspend anode wires.
A further object of the present invention is to provide such a detector that has no standoffs or studs or any other wire supporting parts mounted on the bottom of detector: either conductive or dielectric.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.